System and method for magnetic resonance imaging reconstruction using novel k-space sampling sequences

ABSTRACT

A system and method for magnetic resonance imaging reconstruction using novel k-space sampling sequences is provided. The method includes dividing k-space into a plurality of regions along a dividing direction; scanning an object using a plurality of sampling sequences; acquiring a plurality of groups of data lines; filling the plurality of groups of data lines into the plurality of regions of the k-space; and reconstructing an image based on the filled k-space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage under 35 U.S.C. § 371 ofInternational Application No. PCT/CN2016/085412, filed on Jun. 12, 2016,designating the United States of America, which claims priority ofChinese Patent Application No. 201510437221.X filed Jul. 23, 2015, andChinese Patent Application No. 201510719200.7 filed Oct. 29, 2015, theentire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure generally relates to magnetic resonance imaging(MRI), and more particularly, to a system and method for dataacquisition and data processing in MRI.

BACKGROUND

Magnetic resonance imaging (MRI) is a widely used medical techniquewhich produces images of a region of interest (ROI) by exploiting apowerful magnetic field and radio frequency (RF) techniques. During anMRI process, the acquired signals may be processed and filled into thek-space, then data in the k-space may be transformed to reconstruct MRIimages. A fast spin echo (FSE) sequence may be used in an MRI process.During the filling process, the k-space may be divided into severalregions. Echoes from different echo trains but in the same position ofeach echo train may be filled into the same region, and echoes from thesame echo train may be filled into different regions. Because of T2relaxation, a blur may occur in the final reconstructed image. Inaddition, during a repetition time, if a slight movement of the targetoccurs, motion artifacts may appear in the reconstructed image.Therefore, it is desirable to suppress the motion artifacts effectivelyand to make the image clearer.

SUMMARY

In a first aspect of the present disclosure, a method for generating amagnetic resonance (MR) image is provided. The method may include one ormore of the following operations. A k-space may be divided into aplurality of regions along a dividing direction. The plurality ofregions may include at least a first region including a center of thek-space and a second region different from the first region. An objectmay be scanned using a plurality of sampling sequences. A plurality ofgroups of data lines may be acquired. A group of data lines of theplurality of groups may correspond to one of the plurality of samplingsequences, and the group of data lines may be filled into one region ofthe plurality of regions. A data line may include a plurality of echosignals corresponding to a plurality of echo times respectively. Theplurality of groups of data lines may be filled into the plurality ofregions of the k-space along one or more filling directions. The fillingdirection of at least a portion of the first region may be opposite tothe filling direction of at least a portion of the second region. Animage may be reconstructed based on the plurality of groups of datalines filled into the k-space.

In a second aspect of the present disclosure, a method for generating amagnetic resonance (MR) image is provided. The method may include one ormore of the following operations. A k-space may be divided into aplurality of regions along a dividing direction. The plurality ofregions may include a first region and a second region. The first regionor/and the second region may include at least portion of a center of thek-space. An object may be scanned using a plurality of samplingsequences. A plurality of groups of data lines may be acquired. A groupof data lines of the plurality of groups may correspond to one of theplurality of sampling sequences, and the group of data lines may befilled into one region of the plurality of regions. A data line mayinclude a plurality of echo signals corresponding to a plurality of echotimes respectively. The plurality of groups of data lines may be filledinto the plurality of regions of the k-space along one or more fillingdirections. The filling direction of at least a portion of the firstregion may be opposite to the filling direction of at least a portion ofthe second region. An image may be reconstructed based on the pluralityof groups of data lines filled into the k-space.

In a third aspect of the present disclosure, a system for generating amagnetic resonance (MR) image is provided. The system may include aregion division block configured to divide k-space into a plurality ofregions along a dividing direction, wherein the plurality of regions mayinclude at least a first region including a center of the k-space; anMRI scanner configured to scan an object using a plurality of samplingsequences and to acquire a plurality of groups of data lines, wherein agroup of data lines of the plurality of groups may correspond to one ofthe plurality of sampling sequences, and the group of data lines may befilled into one region of the plurality of regions, and a data line Agroup of data lines of the plurality of groups may correspond to one ofthe plurality of sampling sequences, and the group of data lines may befilled into one region of the plurality of regions; a filling blockconfigured to fill the plurality of groups of data lines into theplurality of regions of the k-space along one or more fillingdirections, wherein the filling direction of at least a portion of thefirst region may be opposite to the filling direction of at least aportion of the second region; and an image reconstruction blockconfigured to reconstruct an image based on the plurality of groups ofdata lines filled into the k-space.

In some embodiments, the dividing direction may include a first phaseencoding direction, a second phase encoding direction, a linearcombination of the first phase encoding direction and the second phaseencoding direction, or a radial direction.

In some embodiments, a first direction may be along the dividingdirection or opposite to the dividing direction, and a second directionmay be opposite to the first direction.

In some embodiments, the plurality of groups of data lines may include afirst group of data lines and a second group of data lines. The firstgroup of data lines may be filled into the first region along the firstdirection, and the second group of data lines may be filled into thefirst region along the second direction.

In some embodiments, the first group of data lines and the second groupof data lines are symmetric with respect to the center of the k-space.

In some embodiments, the first group of data lines and the second groupof data lines may include one or more data lines with a same phaseencoding. In some embodiments, a weighted averaging process may beperformed on the one or more data lines with the same phase encoding.

In some embodiments, the plurality of groups of data lines may include athird group of data lines and a fourth group of data lines. A firstportion of the first region may abut a second portion of the secondregion. The third group of data lines may be filled into the firstportion along the first direction, and the fourth group of data linesmay be filled into the second portion along the second direction.

In some embodiments, the second region may be divided into a pluralityof portions. The plurality of portions may include a third portion and afourth portion that may abut the third portion. A fifth group of datalines of may be filled into the third portion along the first direction,and a sixth group of data lines may be filled into the fourth portionalong the second direction.

In some embodiments, a correction may be performed on at least somegroups of the plurality of groups of data lines based on the echo timesof the echo signals.

In some embodiments, a fifth portion which is filled with a seventhgroup of data lines along the first direction in a third region of theplurality of regions may be identified. An eighth group of data linesmay be obtained. The eighth group of data lines may be filled into thefifth portion of the third region along the second direction. A weightedaveraging process may be performed on the seventh group of data linesand the eighth group of data lines.

In some embodiments, the plurality of groups of data lines may includeat least three groups of data lines. Two groups of data lines of thethree groups of data lines may include a data line corresponding to zerophase encoding, phase encodings of the other one group of data lines ofthe three groups of data lines may be larger than or less than the zerophase encoding.

In some embodiments, two groups of data lines using two samplingsequences may be acquired. The filling directions of the two groups oflines may be the same or opposite. The two groups of data lines mayinclude one or more data lines with a same phase encoding.

In some embodiments, the sampling sequence may include a fast spin echosequence, a half-Fourier acquisition single-shot turbo spin-echo, aturbo gradient spin echo sequence, or an echo planar imaging sequence.

In some embodiments, the second region may not include the center of thek-space.

In some embodiments, the first region and the second region arepartially overlapped with each other.

In some embodiments, each group of data lines of the plurality of groupsof data lines may include a same number of data lines.

Additional features will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the artupon examination of the following and the accompanying drawings or maybe learned by production or operation of the examples. The features ofthe present disclosure may be realized and attained by practice or useof various aspects of the methodologies, instrumentalities andcombinations set forth in the detailed examples discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is further described in terms of exemplaryembodiments. These exemplary embodiments are described in detail withreference to the drawings. These embodiments are non-limiting exemplaryembodiments, in which like reference numerals represent similarstructures throughout the several views of the drawings, and wherein:

FIG. 1 is a block diagram depicting a magnetic resonance imaging (MRI)system according to some embodiments of the present disclosure;

FIG. 2 is a block diagram depicting an MRI system according to someembodiments of the present disclosure;

FIG. 3 is a flowchart illustrating a process for MRI according to someembodiments of the present disclosure;

FIG. 4-A is a block diagram illustrating an architecture of a processingmodule according to some embodiments of the present disclosure;

FIG. 4-B is a flowchart illustrating a process for processing MR signalsaccording to some embodiments of the present disclosure;

FIG. 5 is a block diagram illustrating an architecture of an imageproducing unit according to some embodiments of the present disclosure;

FIG. 6 is a flowchart illustrating a process for producing imagesaccording to some embodiments of the present disclosure;

FIG. 7 shows an exemplary diagram of a FSE sequence in a singlerepetition time (TR) according to some embodiments of the presentdisclosure;

FIG. 8-A and FIG. 8-B show an exemplary diagram of a k-space fillingmodel as known in the prior art;

FIG. 9-A and FIG. 9-B illustrate an exemplary method for dividing thek-space according to some embodiments of the present disclosure;

FIG. 10-A and FIG. 10-B illustrate an exemplary method for dividing thek-space according to some embodiments of the present disclosure;

FIG. 11 illustrates filling data lines into the k-space according tosome embodiments of the present disclosure;

FIG. 12 illustrates filling data lines into the k-space according tosome embodiments of the present disclosure;

FIG. 13-A and FIG. 13-B illustrate filling echoes into the k-spaceaccording to some embodiments of the present disclosure;

FIG. 14-A and FIG. 14-B illustrate filling echoes into the regionincluding the center of the k-space according to some embodiments of thepresent disclosure;

FIG. 15-A and FIG. 15-B illustrate filling echoes into the region notincluding the center of the k-space according to some embodiments of thepresent disclosure;

FIG. 16-A and FIG. 16-B illustrate the correction of k-space dataaccording to some embodiments of the present disclosure;

FIG. 17-A through FIG. 17-D illustrate four exemplary images producedfrom data acquired from the abdomen with different image producingprocedures according to some embodiments of the present disclosure; and

FIG. 18-A and FIG. 18-B illustrate two exemplary images produced fromdata acquired from the neck with different image producing proceduresaccording to some embodiments of the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth by way of examples in order to provide a thorough understanding ofthe relevant disclosure. However, it should be apparent to those skilledin the art that the present disclosure may be practiced without suchdetails. In other instances, well known methods, procedures, systems,components, and/or circuitry have been described at a relativelyhigh-level, without detail, in order to avoid unnecessarily obscuringaspects of the present disclosure. Various modifications to thedisclosed embodiments will be readily apparent to those skilled in theart, and the general principles defined herein may be applied to otherembodiments and applications without departing from the spirits andscope of the present disclosure. Thus, the present disclosure is notlimited to the embodiments shown, but to be accorded the widest scopeconsistent with the claims.

It will be understood that the term “system,” “unit,” “module,” and/or“block” used herein are one method to distinguish different components,elements, parts, section or assembly of different level in ascendingorder. However, the terms may be displaced by other expression if theymay achieve the same purpose.

It will be understood that when a unit, module or block is referred toas being “on,” “connected to” or “coupled to” another unit, module, orblock, it may be directly on, connected or coupled to the other unit,module, or block, or intervening unit, module, or block may be present,unless the context clearly indicates otherwise. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

The terminology used herein is for the purposes of describing particularexamples and embodiments only, and is not intended to be limiting. Asused herein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “include,”and/or “comprise,” when used in this disclosure, specify the presence ofintegers, devices, behaviors, stated features, steps, elements,operations, and/or components, but do not exclude the presence oraddition of one or more other integers, devices, behaviors, features,steps, elements, operations, components, and/or groups thereof.

FIG. 1 is a block diagram of a magnetic resonance imaging systemaccording to some embodiments of the present disclosure. As illustrated,an MRI system 100 may include an MRI scanner 110, a control module 120,a processing module 130, and a display module 140. The MRI scanner 110may include a magnet module 111 and a radio frequency (RF) module 112.The magnet module 111 may include a main magnet filed generator and/or agradient magnet field generator (not shown in FIG. 1). The main magnetfield generator may create a static magnetic field B0 during an MRIprocess. The main magnet may be of various types including, for example,a permanent magnet, a superconducting electromagnet, a resistiveelectromagnet, etc. The gradient magnet field generator may generatemagnet field gradients to the main magnet field B0 in the X, Y, and/or Zdirections. The gradient magnet field may encode the spatial informationof a subject located in the MRI scanner 110. The RF module 112 mayinclude RF transmitting coils and/or receiving coils. These RF coils maytransmit RF signals to or receive RF signals from a subject of interest.In some embodiments, the function, size, type, geometry, position,amount, and/or magnitude of the magnet module 111 and/or of the RFmodule 112 may be determined or changed according to one or morespecific conditions. For example, according to the difference infunction and size, the RF coils may be classified as volume coils andlocal coils. In some embodiments of the present disclosure, the volumecoils may include birdcage coils, transverse electromagnetic coils,surface coils, saddle coils, etc. In some embodiments of the presentdisclosure, the local coils may include birdcage coils, solenoid coils,saddle coils, flexible coils, etc. In some embodiments, the magnetmodule 111 and the radio frequency (RF) module 112 may be designed tosurround a subject to form a tunnel type MRI scanner 150 (i.e. aclose-bore MRI scanner), or an open MRI scanner (i.e. an open-bore MRIscanner).

The control module 120 may control the magnet module 111 and/or the RFmodule 112 of the MRI scanner 110, the processing module 130, and/or thedisplay module 140. The control module 120 may receive information fromor send information to the MRI scanner 110, the processing 130, and/orthe display module 140. According to some embodiments of the presentdisclosure, the control module 120 may receive commands from the displaymodule 140 provided by, e.g., a user, and adjust the magnet module 111and/or RF module 112 to take images of a subject of interest accordingto the received commands. The processing module 130 may processdifferent kinds of information received from different modules.

For further understanding the present disclosure, several examples aregiven below, but the examples do not limit the scope of the presentdisclosure. For example, in some embodiments, the processing module 130may process MR signals received from the RF module 112 and generate oneor more MR images based on these signals and deliver the images to thedisplay module 140. In some embodiments, the processing module 130 mayprocess data input by a user or an operator via the display module 140and transform the data into specific commands, and supply the commandsto the control module 120. The display module 140 may receive inputand/or display output information. The input and/or output informationmay include programs, software, algorithms, data, text, number, images,voice, or the like, or any combination thereof. For example, a user oran operator may input some initial parameters or conditions to initiatea scan. As another example, some information may be imported from anexternal resource, such as a floppy disk, a hard disk, a wirelessterminal, or the like, or any combination thereof. In some embodiments,the control module 120, the processing module 130, and/or the displaymodule 140 may be integrated into an MRI console 160. Users may setparameters in MRI scanning, control the imaging procedure, view theimages produced through the MRI console 160.

It should be noted that the above description of the MRI system 100 ismerely provided for the purposes of illustration, and not intended tolimit the scope of the present disclosure. For persons having ordinaryskills in the art, multiple variations and modifications may be madeunder the teachings of the present disclosure. For example, the assemblyand/or function of the MRI system 100 may be varied or changed accordingto specific implementation scenarios. Merely by way of example, someother components may be added into the MRI system 100, such as a patientpositioning module, a gradient amplifier module, and other devices ormodules. Note that the MRI system may be a traditional or asingle-modality medical system, or a multi-modality system including,e.g., a positron emission tomography-magnetic resonance imaging(PET-MRI) system, a remote medical MRI system, and others, etc. However,those variations and modifications do not depart from the scope of thepresent disclosure.

FIG. 2 is a block diagram of the MRI system 100 according to someembodiments of the present disclosure. As shown in the figure, the mainfield and shim coils 201 may generate a main magnetic field that may beapplied to an object (also referred to as subject) exposed inside thefield. The main filed and shim coils 201 may also control thehomogeneity of the generated main field. Gradient coils 202 may belocated inside the main field and shim coils 201. The gradient coils 202may generate a second magnetic field or referred to as a gradient field.The gradient coils 202 may distort the main field generated by the mainfield and shim coils 201 so that the magnetic orientations of theprotons of an object may vary as a function of their positions insidethe gradient field. The gradient coils 202 may include X coils, Y coils,and/or Z coils (not shown in the figure). In some embodiments, the Zcoils may be designed based on circular (Maxwell) coils, while the Xcoils and the Y coils may be designed on the basis of the saddle (Golay)coil configuration. The three sets of coils may generate three differentmagnetic fields that are used for position encoding. The gradient coils202 may allow spatial encoding of MR signals for image construction. Thegradient coils 202 may be connected with one or more of an X gradientamplifier 204, a Y gradient amplifier 205, or a Z gradient amplifier206. One or more of the three amplifiers may be connected to a waveformgenerator 216. The waveform generator 216 may generate gradientwaveforms that are applied to the X gradient amplifier 204, the Ygradient amplifier 204, and/or the Z gradient amplifier 204. Anamplifier may amplify a waveform. An amplified waveform may be appliedto one of the coils in the gradient coils 202 to generate a magneticfield in the X-axis, the Y-axis, or the Z-axis, respectively. Thegradient coils 202 may be designed for either a close-bore MRI scanneror an open-bore MRI scanner. In some instances, all three sets of coilsof the gradient coils 202 may be energized and three gradient fields maybe generated thereby. In some embodiments of the present disclosure, theX coils and Y coils may be energized to generate the gradient fields inthe X direction and the Y direction.

RF coils 203 may generate a third magnetic field that is utilized togenerate MR signals for image construction. In some instances, the RFcoils 203 may include a transmitting coil and a receiving coil. In someembodiments, the RF coils 203 may be in connection with RF electronics209 that may be configured or used as one or more integrated circuits(ICs) functioning as a waveform transmitter and/or a waveform receiver.The RF electronics 209 may be connected with an RF amplifier 207 and ananalog-to-digital converter (ADC) 208. The waveform generator 216 maygenerate an RF signal. The RF signal may be first amplified by the RFamplifier 207, processed by the RF electronics 209, and applied on theRF coils 203 to generate a third magnetic field, in addition to themagnetic fields generated by, e.g., the main filed and shim coils 201and the gradient coils 202. In some embodiments of the presentdisclosure, the waveform generator 201 may generate a series of RFwaveforms periodically or aperiodically. For instance, the waveformgenerator 216 may generate an excitation RF pulse with a flip angle of90° and multiple refocusing RF pulses with a flip angle of 180°. Notethat the excitation RF pulse may have a flip angle other than 90°, e.g.,any magnitude ranging from 00 to 1800. An excitation RF pulse with aflip angle of 90° is mentioned elsewhere in the present disclosure forillustration purposes, and is not intended to limit the scope of thepresent disclosure. An excitation RF pulse with a flip angle other than90° may be used.

As described elsewhere in the present disclosure, the flip angle of arefocusing RF pulse may be of a value other than 180°. Furthermore, thewaveform generator 216 may generate a series of RF waveformsperiodically or aperiodically. For instance, the waveform generator 216may generate an excitation RF pulse with a flip angle of 90° andmultiple refocusing RF pulses with same flip angles or variable flipangles. The flip angle of the excitation RF pulse may be variable aswell. The excitation RF pulse may be utilized to generate the thirdmagnetic field, and with the application of one or more refocusing RFpulses, one or more MR signals may be generated. For instance, an echotrain with multiple echoes may be generated. The echo train length (ETL)may be either fixed or variable. For instance, for a same tissue to beimaged, ETL may be fixed. For different tissues, ETL may be variable.Furthermore, even for a same tissue, ETL may be variable. The echo trainmay be received by the receiving coils of the RF coils 203. Then theecho train may be sent to the RF electronics 209, and transmitted to theADC 208 for digitization. The echo train may be demodulated and filteredin the electronics 209. Subsequently, the echo train may be processed byan image processor 211, e.g., with the assistance of the CPU 213, togenerate one or more images. A console 214 may communicate through alink with the CPU 213 and allow one or more operators to control theproduction and/or display of images on image display 212. The console214 may include an input device, a control panel (not shown in thefigure), etc. The input device may be a keyboard, a touch screen, amouse, a remote controller, or the like, or any combination thereof.

The CPU 213 may control the production of the waveforms in the waveformgenerator 216, and the production of images in the image processor 211.The CPU 213 may be a central processing unit (CPU), anapplication-specific integrated circuit (ASIC), an application-specificinstruction-set processor (ASIP), a graphics processing unit (GPU), aphysics processing unit (PPU), a microcontroller unit, a digital signalprocessor (DSP), a field programmable gate array (FPGA), an ARM, or thelike, or any combination thereof.

The data storage 215 may store received MR signals. When an MRI scan iscompleted and the whole data of a scanned object (e.g., a tissue or aspecific part of a body) is acquired. A Fourier transform of the datamay be performed by, without limitation to, the CPU 213, the imageprocessor 211, or the like, or any combination thereof. After thetransform is completed, one or more desired images may be generated. Theimages may be stored in the data storage 215. The images may be furtherconveyed to the image display 212 for display. A shim control 210 may beutilized to control the homogeneity of the main magnetic field generatedby the main field and shim coils 201.

It should be noted that the above description of the MRI system ismerely provided for the purposes of illustration, and not intended tolimit the scope of the present disclosure. For persons having ordinaryskills in the art, multiple variations and modifications may be madeunder the teaching of the present invention. However, those variationsand modifications do not depart from the scope of the presentdisclosure.

FIG. 3 depicts a flowchart of an MR scan that may be performed accordingto some embodiments of the present disclosure. In step 301, one or moreprotocols may be selected. A protocol may be designed for one or moretissues to be imaged, diseases, and/or clinical scenarios. A protocolmay contain a certain number of pulse sequences oriented in differentplanes and/or with different parameters. The pulse sequences may includea spin echo sequence, a gradient echo sequence, a diffusion sequence, aninversion recovery sequence, or the like, or any combination thereof.For instance, the spin echo sequences may include fast spin echo (FSE),half-Fourier acquisition single-shot turbo spin-echo (HASTE), turbogradient spin echo (TGSE), or the like, or any combination thereof. Whenan MR scan is to be conducted, an operator may select a protocol for thescan. For example, for a cranial scan, the operator may select any oneof the protocols called “Routine Adult Brain,” “MR Angiogram Circle ofWillis,” and many others. These protocols described above or otherprotocols may be stored in the data storage 215 as illustrated in FIG.2, or other storage devices (e.g., an external storage device or serveraccessible by the MR system 100).

Parameters may be set in step 302. The parameters may be set via theconsole 214 through a user interface that may be displayed on, e.g., theimage display 212 as specified in FIG. 2. The parameters may includeimage contrast and/or ratio, a region of interest (ROI), slicethickness, an imaging type (e.g., T1 weighted imaging, T2 weightedimaging, proton density weighted imaging, etc.), T1, T2, a spin echotype (spin echo, fast spin echo (FSE), fast recovery FSE, single shotFSE, gradient recalled echo, fast imaging with stead-state procession,and so on), a flip angle value, acquisition time (TA), echo time (TE),repetition time (TR), echo train length (ETL), the number of phases, thenumber of excitations (NEX), inversion time, bandwidth (e.g., RFreceiver bandwidth, RF transmitter bandwidth, etc.), or the like, or anycombination thereof.

According to some embodiments of the present disclosure, the term“phase” may refer to a segment, section, part or fragment of a series offlip angles (or a flip angle schedule) corresponding to an echo traindivided according to some principles. The number of phase(s) and/or thenumber of echo(es) in each phase may depend on specific conditions. Insome embodiments, an echo train may be divided into several phasesaccording to considerations including, e.g., the characteristics of areference signal schedule, a desired signal evolution, etc. Merely byway of example, the reference signal schedule of an echo train may bedivided into three segments, regardless of what their values are or howtheir trends vary (e.g. firstly exponential decay, secondly essentiallyflat, and lastly exponential decay again), then the echo train may bedivided into three phases accordingly. In some embodiments, thereference signal schedule may be divided into different phases accordingto one or more other considerations. For example, only one or severalspecific echo(es) associated with resultant signal(s) of interest needto be paid attention to. For example, it is desired that the signalscorresponding to two echoes meet one or more thresholds; the echo trainmay belong to a single phase so that the two echoes of interest arelocated in the same phase; the echo train may be divided into two ormore phases, and the two echoes of interest may be located in a samephase or different phases. In some embodiments, there may be noreference signal schedule at all, and the number of phase(s) and/or thenumber of echo(es) in each phase may be determined based on, e.g., arandom division, an equal division, a certain rule, or the like, or anycombination thereof. The certain rule may include Arithmeticprogression, Geometric progression, Cauchy sequence, Farey sequence,look-and-say sequence, or the like, or a variation thereof, or anycombination thereof.

It should be noted that the above description of the MRI system 100 ismerely provided for the purposes of illustration, and not intended tolimit the scope of the present disclosure. For persons having ordinaryskills in the art, multiple variations and modifications may be madeunder the teachings of the present disclosure. For example, the numberof phases in an echo train may be one, two, three, or more, or equal tothe number of echoes. In some embodiments, several echoes may be locatedin one phase, and the remaining echoes belong to one or more otherphases or are not assigned to a phase at all. However, those variationsand modifications do not depart from the scope of the presentdisclosure.

Preparation for the MR scan may be performed in step 303. Thepreparation may include placing an object, e.g., a selected portion of asubject of interest, within the scanning area, setting the scanningrange, tuning and matching shimming coils, adjusting a center frequency,adjusting transmitter attenuation/gain, adjusting signal receptionattenuation/gain, setting dummy cycles, or the like, or any combinationthereof.

The selected portion of a subject of interest may be scanned in step304. The scanning may include localizer scans, calibration scans forparallel imaging, automatic pre-scan, or the like, or any combinationthereof. For instance, the localizer scans may produce localizer imagesof low resolution and a large field of view (FOV). Such localizer imagesmay be utilized in subsequent steps. In this step, a pulse sequenceincluding, for example, an excitation RF pulse and a series ofrefocusing RF pulses, may be applied on the selected portion. The flipangles of the refocusing RF pulses may be either fixed or variable.

MRI is a non-invasive imaging technique that uses a powerful main magnetfield to align the nucleus spins in a subject (or a portion thereof).When the subject is exposed in a magnetic field (main magnet field B0),the nucleus spins of the subject tend to align with field B0, but maystill precess at the Larmor frequency. The overall motion of the nucleusspins in the subject, subject to field B0, may be simplified as netmagnetization (M) that is the averaged sum of many individual nucleusspins. The net magnetization M may be broken down into a longitudinalcomponent (along the Z axis, aligned with field B0), and a transversecomponent (within the XY plane). With the effect of main magnet fieldB0, M may constitute a longitudinal magnetization vector in themacroscopic angle. A second magnetic field, RF field (field B1), may beapplied to M, oscillating the Larmor frequency, and causing M to precessaway from the field B0 direction. During the excitation by radiofrequency, longitudinal magnetization may decrease and transversemagnetization may appear. Merely by way of example, if an excitation RFpulse with a 90° flip angle is applied, when the RF transmitter isturned off, there is no longitudinal magnetization any more, and onlytransverse magnetization exists. The transverse magnetization may inducea current signal in the RF receiving coils, and the induced current maybe referred to as an MR signal. The MR signal may correspond to one ormore echo trains including, for example, one or more echo signals,according to the pulse sequence selected in step 301.

Generated MR signals may be received in step 305. Step 305 may beperformed by the RF coils 203 as described in FIG. 2. The MR signals maycorrespond to one or more echo trains, or the like. It should be notedthat step 305 and step 304 may be repeated until sufficient data togenerate an image is acquired or an image is generated. One or moreoperations may be performed on the MR signals to produce images of theselected portion. The operations may further include Fourier transform(FT) of the data in k-space, frequency encoding, phase encoding, or thelike, or any combination thereof. The operations may include fillingdata of the MR signals into the Fourier domain (or referred to as thespatial frequency space, or the k-space). For instance, Fouriertransform may be a fast Fourier Transform (FFT), a 2-dimensional FT, a3-dimensional FT, or the like, or any combination thereof. In step 306,one or more images of the selected portion may be produced. The imagesmay be displayed on, e.g., the image display 212 (shown in FIG. 2), orother display devices (e.g., an external display device).

It should be noted that the flowchart described above is provided forthe purposes of illustration, not intended to limit the scope of thepresent disclosure. For persons having ordinary skills in the art,multiple variations and modifications may be reduced to practice in thelight of the present disclosure. However, those variations andmodifications do not depart from the scope of the present disclosure.For instance, step 301, step 302, and step 303 may be performedsequentially at an order other than that described above in connectionwith FIG. 3. Alternatively, step 301, step 302, and step 303 may beperformed concurrently.

FIG. 4-A is a block diagram illustrating the processing module 130according to some embodiments of the present disclosure. The processingmodule 130 as illustrated in FIG. 1 may process information before,during, or after an imaging procedure. Note that the construction of theprocessing module 130 may have some other variations, and that FIG. 4Ais provided for illustration purposes. The processing module 130 mayinclude a CPU. The CPU may be a central processing unit (CPU), anapplication-specific integrated circuit (ASIC), an application-specificinstruction-set processor (ASIP), a graphics processing unit (GPU), aphysics processing unit (PPU), a microcontroller unit, a digital signalprocessor (DSP), a field programmable gate array (FPGA), an ARM, or thelike, or any combination thereof. As shown in FIG. 4-A, the processingmodule 130 may include a computing unit 401, an image producing unit402, a storage unit 403, and an A/D converter.

The computing unit 401 may calculate different kinds of informationgenerated from the MRI scanner 110, or received from the control module120 and/or display module 140. The information from the MRI scanner 110may be a plurality of MR signals of a subject. The information from thecontrol module 120 may include information about the MRI scanner 110,the magnet module 111, a patient position (e.g., within an MRI system),the RF module 112, or the like, or any combination thereof. In someembodiments, the information may be a patient position, the main and/orgradient magnet intensity, the radio frequency phase and/or amplitude,and so on. The information from the display module 140 may includeinformation from a user and/or other external resource. Exemplaryinformation from a user may include parameters regarding image contrastand/or ratio, a subject of interest (e.g., the type of tissue to beimaged, etc.), slice thickness, an imaging type (e.g., T1 weightedimaging, T2 weighted imaging, proton density weighted imaging, etc.),T1, T2, a spin echo type (e.g., spin echo, fast spin echo (FSE), fastrecovery FSE, single shot FSE, gradient recalled echo, fast imaging withstead-state procession, and so on), a flip angle value, acquisition time(TA), echo time (TE), repetition time (TR), echo train length (ETL), thenumber of phases, the number of excitations (NEX), inversion time,bandwidth (e.g., RF receiver bandwidth, RF transmitter bandwidth, etc.),or the like, or any combination thereof.

The image producing unit 402 may process the data such as magneticresonance (MR) signals acquired from the subject of interest andreconstruct them into an MR image. The image producing unit 402 mayspatially decode an MR signal that has been spatially encoded by themagnetic field(s). The intensity or magnitude of the signal, and otherproperties such as a phase number, a relaxation time (T1 or T2),magnetization transfer, or the like, may be ascertained. The imageproducing unit 402 may employ different kinds of imaging reconstructiontechniques for the image reconstruction procedure. Exemplary imagereconstruction techniques may include Fourier reconstruction,constrained image reconstruction, regularized image reconstruction inparallel MRI, or the like, or a variation thereof, or any combinationthereof.

The storage unit 403 may store the information that may be used by thecomputing unit 401 and/or the image producing unit 402. The informationmay include programs, software, algorithms, data, text, number, imagesand some other information. These examples are provided here forillustration purposes, and not intended to limit the scope of thepresent disclosure. Algorithms stored in the storage unit 403 mayinclude recursion, a bisection method, an exhaustive search (orbrute-force search), a greedy algorithm, a divide and conquer algorithm,a dynamic programming method, an iterative method, a branch-and-boundalgorithm, a backtracking algorithm, or the like, or any combinationthereof. In some embodiments, the storage unit 403 may store MR signals.In some embodiments, the storage unit 403 may share the same storagewith the data storage 215 in FIG. 2.

The A/D converter 404 may convert analog MR signals to digital MRsignals. In some embodiments, one or more parameters may be set beforeor during the conversion, e.g., voltage, current, rate, samplingfrequency, or the like, or a combination thereof. The converted MRsignals may be stored in the storage unit 403 or the data storage 215.

It should be noted that the above description of the processing module130 is merely provided for the purposes of illustration, and notintended to limit the scope of the present disclosure. For personshaving ordinary skills in the art, multiple variations or modificationsmay be made under the teachings of the present disclosure. For example,the assembly and/or function of processing unit may be varied orchanged. In some embodiments, the computing unit 401 and the imageproducing unit 402 may share one storage unit 403. While in someembodiments, the computing unit 401 and the image producing unit 402 mayhave their own storage blocks, respectively. However, those variationsand modifications do not depart from the scope of the presentdisclosure.

FIG. 4-B is a flowchart illustrating a process for processing MR signalsaccording to some embodiments of the present disclosure. In step 411,echo signals may be acquired. The echo signals may be acquired by theMRI scanner 110, or may be read from the data storage 215, or anexternal resource including, for example, a floppy disk, a hard disk, awired terminal, a wireless terminal, or the like, or any combinationthereof. The echo signals acquired may be phase encoded, and/orfrequency encoded. The echo signals may be acquired from a plurality ofshots of a RF pulse sequence. In some embodiments, the echo signals maybe acquired in different orders, for example, the echo signals ofrelatively lower phases may be acquired first, and that of higher phasesmay be acquired subsequently. The acquired echo signals may be analog ordigital. In some embodiments, the analog echo signals acquired may beconverted from analog signals to digital signals in step 412. Theanalog-to-digital conversion may be performed by the A/D converter 404.The digitized echo signals may include a plurality of data points,wherein each data point may have a specific spatial frequency (i.e., aspecific phase and a specific frequency). Further, each data pointdigitized from the echo signals may be a complex number with real andimaginary components. Alternately, each data point may be defined ashaving one or more factors, e.g., amplitude, phase, or the like. In someembodiments, the amplitude and phase of a data point may be computed bya trigonometric relation. The digitized echo signals may be furtherstored in step 413. The digitized echo signals may be stored in the datastorage 215 of the MRI system, the storage unit 403 of the processingmodule 130, or an external storage medium including, for example, afloppy disk, a hard disk, a wired terminal, a wireless terminal, or thelike, or any combination thereof.

Then the echo signals may be computed in step 414. Computation of theecho signals may include a Fourier transform, an interconversion of thedata in Cartesian coordinate system and data in polar coordinate system(i.e., an interconversion of data with real and imaginary components anddata with amplitude and phase components). In some embodiments,computation may be performed to correct the echo signals. Computation ofthe echo signals may include weighted calculation, averaging,optimization, data filtering, data screening, or the like, or acombination thereof. The computation process may be performed by thecomputing unit 401.

Afterwards, the echo signals may be used to produce an MR image in step415. Generally, the echo signals may be filled into the k-space,processed by one or more algorithms, and an image may be reconstructed.The image may be produced by the image producing unit 402. In someembodiments, during the imaging producing, the process may return tostep 414 for obtaining data until a complete image is produced.

It should be noted that the above description of the flowchart in FIG.4-B is merely provided for the purposes of illustration, and notintended to limit the scope of the present disclosure. For personshaving ordinary skills in the art, multiple variations or modificationsmay be made under the teachings of the present disclosure. For example,the storage of the echo signals in step 413 may be not necessary.Alternatively, an image storage step may be added after step 415. Asanother example, the computation step 414 may be combined with the imageproducing step 415. However, those variations and modifications do notdepart from the scope of the present disclosure.

FIG. 5 is a block diagram illustrating an architecture of the imageproducing unit 402 according to some embodiments of the presentdisclosure. The image producing unit 402 may include a region divisionblock 501, a filling block 502, a correction block 503, and an imagereconstruction block 504. The region division block 501 may divide thek-space into a plurality of regions. In some embodiments, the number ofthe regions may be fixed or variable. The number of the regions may beset by the default of the system, or may be adjusted for the scanning ofdifferent ROIs of a subject, or the same or different ROIs of differentsubjects. In some embodiments, the size of any region in the k-space maybe fixed or variable. In some embodiments, the sizes of the plurality ofregions may be the same as or different from each other. In someembodiments, the plurality of the regions may be divided along adividing direction. The dividing direction may be the phase encodingdirection ky or kz, or any linear combination direction of ky and kz(e.g., the radial orientation kr). For example, when the plurality ofthe regions may be divided along the phase encoding direction, the phaseencoding of the k-space may include a plurality of phase encoding linesillustrated as a set {PE1, PE2, . . . , PEi, . . . , PEN, PE1<PE2< . . .<PEi< . . . <PEN, i<N}, and a plurality of regions with the phaseencoding ranges of PE1˜PEi, PEi+1˜PEi+x, . . . , PEN−j˜PEN may beobtained after division. As used herein, PE refers to “phase encoding.”Any one of N, i, x, and j may be a real integral number.

In some embodiments, for two adjacent regions among the plurality ofregions, their phase encoding ranges may partially overlap. As usedherein, the phrase “two adjacent regions” may represent that one regionabuts the other region. In some embodiments, for two adjacent regionsamong the plurality of regions, their phase encoding ranges do notoverlap. Merely by way of example, the phase encoding ranges of twoadjacent regions a and b are PEi+1˜PEi+x and PEj+1˜PEj+y (j>i, and y isa real integer), respectively; the phase encoding lines of the edges ofthe two regions may satisfy a relationship described by: j+1≤i+x(indicating that the two adjacent regions partially overlap), orj+1=i+x+1 (indicating that the two adjacent regions do not overlap). Insome embodiments, one of the plurality of regions may include the centerof the k-space, which may be illustrated as PE0−i˜PE0+j, where i≥1, j≥1,and i may be to the same as or different from j. In some embodiments,the region including the center of the k-space may be illustrated asPE0−i˜PE0 or PE0˜PE0+j, wherein i≥1, j≥1, and i may be to the same as ordifferent from j.

The filling block 502 may fill echo signals into the plurality ofregions of the k-space. An echo signal may correspond to a phaseencoding line, and the echo signal or data of the echo signal may befilled into a corresponding phase encoding line of a region of thek-space. In some embodiments, the regions of the k-space may be filledin an order according to a system setting. In some embodiments, theregions of the k-space may be filled in an order that is different froma system setting. In some embodiments, the filling order may beconsistent with the phase encoding order, or may be adjusted based onthe priority levels of the regions, or the like, or any combinationthereof. For example, the filling order may be consistent with the phaseencoding order, either from the minimum encoding to the maximumencoding, or from the maximum encoding to the minimum encoding, orrandomly. As used herein, suppose that the range of the k-space alongthe phase encoding direction may be [−127, +128], the minimum encodingmay refer to the phase encoding line of ky=−127, and the maximumencoding may refer to the phase encoding line of ky=+128. As anotherexample, the regions that have a relatively lower phase encoding orlocate close to the center of the k-space may be filled preferentially.As used herein, “preferentially” may indicate that the regions may befilled first, and the other regions may be filled subsequently.

In some embodiments, the order of filling the echo signals or data intothe regions of the k-space may be based on the order the echo signalsare acquired. For example, three echo signals (echo 1, echo 2, and echo3) of an echo train are acquired sequentially; the filling order may bein accordance with the acquisition order (echo 1, echo 2, echo 3), oropposite to the acquisition order (echo 3, echo 2, echo 1). As usedherein, the echo train may refer to an echo line including a pluralityof echoes generated within a single repetition time. As used herein, therepetition time may refer to the time between the applications of twoconsecutive excitation RF pulses.

In some embodiments, the filling may take place at the time the echosignals are acquired. In some embodiments, the echo signals may bestored and subsequently retrieved to be filled into the k-space. In someembodiments, the echo signals of the same echo train may be used to fillinto the same region of the k-space. For instance, there is a regionwith a phase encoding range of PEi+1˜PEi+x (x≥5); three echo signals ina same echo train (echo 1, echo 2, and echo 3) of which the phaseencodings are PEi+1, PEi+3, and PEi+5, respectively; the three echosignals may be filled into the specific sites (or “phase encoding line”)PEi+1, PEi+3, and PEi+5 of the region PEi+1˜PEi+x.

The correction block 503 may correct the echo signals or data filledinto the k-space. For an echo train, the intensity of the echo signalsmay attenuate with the passage of the acquisition time, and theintensity attenuation of the echo signals may cause errors and reducethe image quality. A correction may be performed. For instance, at anadjoining (but not overlapping) region of two adjacent regions, anabrupt intensity change may occur (see, for example, FIG. 12). Acorrection may be performed to avoid or alleviate the abrupt intensitychange. For instance, a weighted averaging process may be performed onthe data to be filled into the adjoining region (see, for example, FIG.16-A and FIG. 16-B). As another example, two adjacent regionsPEi+1˜PEi+x (region 1) and PEj+1˜PEj+y (region 2) (j>i, and j+1≤i+x)partially overlap, forming an overlapping region (see, e.g., FIG. 9-Aand FIG. 9-B). The data (or “echo signals”) filled into the adjacentregions may be from different echo trains generated by the FSE sequence.The overlapping region may be filled with data from different echotrains generated by the FSE sequence (see, e.g., FIG. 11). To reduce oreliminate the data overlapping in the overlapping region, a correctionmay be performed, e.g., a weighting process may be performed.

The image reconstruction block 504 may reconstruct an image according tothe k-space data. Different kinds of techniques may be used for imagereconstruction. In some embodiments, the image reconstruction techniquesmay include but not limited to Fourier reconstruction, inverse Fouriertransform, constrained image reconstruction, regularized imagereconstruction in parallel MRI, or the like, or any combination thereof.

It should be noted that the above description of the block diagram inFIG. 5 is merely provided for the purposes of illustration, and notintended to limit the scope of the present disclosure. For personshaving ordinary skills in the art, multiple variations or modificationsmay be made under the teachings of the present disclosure. For example,the region division block 501 may be not necessary and may be integratedin the filling block 502. As another example, any two of the blocks maybe integrated into a single block. However, those variations andmodifications do not depart from the scope of the present disclosure.

FIG. 6 is a flowchart illustrating a process for producing imagesaccording to some embodiments of the present disclosure. In step 601,the k-space may be divided into a plurality of regions. The regiondivision may be performed by the region division block 501. Theplurality of regions may be divided along a dividing direction. Thedividing direction may be the phase encoding direction ky or kz, or anylinear combination direction of ky and kz (e.g., the radial orientationkr). In some embodiments, the size or shape of the region may be fixedor variable. For example, if in a Cartesian coordinate system, the shapemay be rectangle, square, rhombic, or the like. As another example, ifin a polar coordinate system, the shape may be circular, elliptic,sectorial, ring, or the like. In some embodiments, the plurality ofregions may be continuous along the dividing direction, or one or moreoverlapping regions may occur between any two adjacent regions. The sizeor shape of the overlapping region may be fixed or variable, and thesizes or shapes of the one or more overlapping regions may be the sameor different with each other.

In step 602, echo signals may be acquired. The echo signals may beacquired by the MRI scanner 110, or may be read from the data storage215, the storage unit 403, or an external resource including, forexample, a floppy disk, a hard disk, a wired terminal, a wirelessterminal, or the like, or any combination thereof. The echo signalsacquired may be phase encoded, and/or frequency encoded. The echosignals may be acquired from one or more FSE sequences. In someembodiments, the acquired echo signals may be converted from analogsignals to digital signals.

In step 603, the acquired echo signals may be filled into the pluralityof regions of the k-space. The filling process may be performed by thefilling block 502. The echo signals may be filled into the regions alonga filling direction. The filling direction may be the phase encodingdirection, or opposite to the phase encoding direction. The echo signalsmay be filled into the regions according to a filling order. The fillingorder may be according to a default setting of the system, or may be setby a user (e.g., an operator). In some embodiments, one or more regionsof the k-space may be filled with echo signals generated by one or moreFSE sequences. For a specific region, an echo train including aplurality of echoes (also referred to as echo signals) including echo 1,echo 2, echo 3, . . . , echo N; the echo signals may be filled into theregion sequentially (e.g., from echo 1 to echo N), or in another fillingorder (e.g., from echo N to echo 1). For multiple regions, the filledecho signals may be generated by a plurality of FSE sequences. In someembodiments, the region(s) of which the phase encoding is relatively lowor is close to the center of the k-space may be filled preferentially.As used herein, “preferentially” may indicate that the regions may befilled first, and the other regions may be filled subsequently.

The data (or “echo signal(s)”) filled in the k-space may be corrected instep 604. The correction process may be performed by the correctionblock 503. In some embodiments, the correction may be performed inconnection with the data in an overlapping region. For instance, aweighting process may be performed in an overlapping region. In someembodiments, the intensity of the echo signals may attenuate with thepassage of the acquisition time along the echo train, and the correctionmay be performed to reduce or eliminate the effect of the signalattenuation. For example, two or more sets of echo signals may be filledinto two adjacent regions along opposite filling directions (see, e.g.,FIG. 16-A and FIG. 16-B).

Then an image may be reconstructed in step 605 based on the correcteddata in the k-space in step 604. The image reconstruction process may beperformed by the image reconstruction block 504. The imagereconstruction techniques may include Fourier reconstruction,constrained image reconstruction, regularized image reconstruction inparallel MRI, or the like, or any combination thereof. In someembodiments, if the reconstructed image is not qualified (e.g., thenoise exceeds a threshold, or conspicuous artifacts exist), theprocedure may return to step 604 for further correction, and the step605 and step 604 may be repeated until an qualified image may beconstructed.

It should be noted that the above description of the flowchart in FIG. 6is merely provided for the purposes of illustration, and not intended tolimit the scope of the present disclosure. For persons having ordinaryskills in the art, multiple variations or modifications may be madeunder the teachings of the present disclosure. For example, the regiondivision step 601 may be not necessary, as the region division mannermay be pre-stored in the system. As another example, a process of FSEexcitation may be added in the acquisition step 602 to generatecorresponding echo trains. As another example, data processing may beadded in the correction step 604 to eliminate image artifacts includingGibbs artifact, motion artifact, flow artifact, metal artifact, chemicalshift artifact, partial volume artifact, wrap around artifact, or thelike, or any combination thereof. As another example, a criterion may beset in the correction step 604 or the reconstruction step 605 for imagequality judgement. However, those variations and modifications do notdepart from the scope of the present disclosure.

FIG. 7 shows an exemplary diagram of a FSE sequence in a singlerepetition time (TR) according to some embodiments of the presentdisclosure. As used herein, the repetition time (TR) may refer to thetime between the applications of two consecutive excitation RF pulses.The RF pulse may include an excitation RF pulse 701 and a plurality ofrefocusing RF pulses including a refocusing RF pulse 702, a refocusingRF pulse 703, a refocusing RF pulse 704, and a refocusing RF pulse 705.In some embodiments, the flip angle of the excitation RF pulse 701 maybe 90°. The flip angle of the refocusing RF pulses (702, 703, 704, and705) may be 180°. As used herein, the flip angle is the rotation of thenet magnetization vector by a radio frequency pulse relative to the mainmagnetic field. In some embodiments, the flip angle of the excitation RFpulse may be the same as that of the refocusing RF pulses. For example,because of T2 relaxation, the intensity of each echo in one echo trainmay be different. As used herein, the T2 relaxation may refer to theprogressive dephasing of spinning dipoles following the excitation RFpulse as seen in a spin echo sequence due to one or more tissue-specificcharacteristics. Merely by way of example, the echo train length (ETL)is 4; to decrease the differences among the echoes in a same echo train,the flip angles of the refocusing RF pulses may be set to be values lessthan or equal to 180°, such as 140°, 155°, 165°, 180°, respectively. Asused herein, the echo train length may refer to the number of echoesacquired within a single repetition time. In some embodiments, the flipangles of the refocusing pulses 702, 703, 704, and 705 may be the sameas or different from each other.

As shown in FIG. 7, Gz may represent the slice selection gradient. Insome embodiments, the slice selection gradient may be imposed along anaxis perpendicular to the plane of the desired slice, resulting in alinear variation of potential resonance frequencies in that direction; atailored RF pulse may be applied, of which the frequency components maymatch the range of frequencies contained in the desired slice. Thecombination of the slice selection gradient and the RF pulse may insurethat the desired slice is excited. Following the excitation RF pulse701, a plurality of refocusing RF pulses (702, 703, 704, and 705) may betransmitted to generate a plurality of echoes (e.g., echo 1, echo 2,echo 3, and echo 4). The number of echoes generated may be determined bythe number of refocusing RF pulses. As illustrated in FIG. 7, the echo 1may be generated by the refocusing RF pulse 702, the echo 2 may begenerated by the refocusing RF pulse 703, the echo 3 may be generated bythe refocusing RF pulse 704, and the echo 4 may be generated by therefocusing RF pulse 705. In some embodiments, Gx may represent thefrequency encoding gradient, and Gy may represent the phase encodinggradient. The frequency encoding gradient and the phase encodinggradient may be used to spatially encode the echoes. For example, beforethe acquisition of the echo 1, the phase encoding gradient 721 may beapplied. The phase encoding gradient 721′ may be applied to adjust theecho 1 when the acquisition of echo 1 is complete. For example, thephase encoding gradient 721′ may be used to eliminate the effects causedby the phase encoding gradient 721. During the acquisition of the echo1, the frequency encoding gradient 731 may be applied. With thefrequency encoding gradient and the phase encoding gradient, the echo 1may be spatially encoded. A spatially encoded echo may correspond to ak-space trajectory and may be used to perform k-space sampling andconstruct MR images subsequently. According to the encoding gradients inFIG. 7, a Cartesian trajectory may be generated.

As shown in FIG. 7, each echo in an echo train may be acquired with adifferent echo time (TE). As used herein, an echo train may refer to aplurality of echoes generated in a single repetition time. As usedherein, the echo time (TE) may refer to the time from the center of thefirst RF pulse (e.g., the excitation RF pulse) in a single repetitiontime to the center of the echo. FIG. 7 shows that, within a singlerepetition time, the echo time of the echo 1 may be shortest, while theecho time of the echo 4 may be longest. In some embodiments, the echoesfilled into the center of the k-space may affect the image contrast andfinal image quality. The time between the middle of an excitation RFpulse and the middle of the echoes filled into the center of the k-spacemay be referred to as effective echo time (effective TE, or TEeff). Insome embodiments, by adjusting the phase encoding gradient, any one ofthe echoes in the echo train may be filled into the center of thek-space.

In some embodiments, because of T2 relaxation, the signal intensity ofeach echo of an echo train may be different. As shown in FIG. 7, withina TR, the signal intensity of the echo 1 may be strongest, and while thesignal intensity of the echo 4 may be weakest. According to the dashline shown in FIG. 7, the differences between the two adjacent echoeswithin a TR may diminish along with time. In some embodiments, thedifference between the two adjacent echoes may be decreased by adjustingthe flip angle of the refocusing RF pulse.

It should be noted that the above description about encoding gradientsis merely provided for the purposes of illustration, and not intended tolimit the scope of the present disclosure. For persons having ordinaryskills in the art, multiple variations and modifications may be madeunder the teaching of the present invention. There may be differenttrajectories and different filling orders by adjusting the frequencyencoding gradient and the phase encoding gradient. For example, in someembodiments, when an echo is being acquired, both of the frequencygradient and the phase gradient may be applied to generate anon-Cartesian k-space trajectory. The non-Cartesian trajectory may beradial, spiral, zigzag, propeller, or the like, or any combinationthereof. However, those variations and modifications do not depart fromthe scope of the present disclosure.

FIG. 8-A shows an exemplary diagram of a k-space filling model for anFSE sequence as known in the prior art. As shown in FIG. 8-A, kx mayrepresent the frequency encoding direction, ky may represent the phaseencoding direction. In the k-space filling model illustrated in FIG.8-A, L echoes may be generated in a single repetition time, and thek-space may be divided into L regions, including region 1, region 2, . .. , region L. N echoes may be filled into each region (for brevity, 1,2, 3, . . . , N as illustrated). In each region, the number of the phaseencoding lines may be N, and the total number of the phase encodinglines may be S. The mathematical relationship of N and S may beexpressed as N=S/L. As illustrated in FIG. 8-A, i may represent theserial number of the echo train which the acquired echo is belong to;the same i may represent that the acquired echoes are from the same echotrain. As shown in FIG. 8-A, during the filling process, echoes from thesame echo train may be filled into different regions. For instance,echoes from the echo train 1 are filled into the region 1, region 2, . .. , region L respectively. As shown in FIG. 8-A, during the fillingprocess, echoes from different echo trains but in the same position ofeach echo train may be filled into the same region. For instance, thenth echo from the echo train 1, the nth echo from the echo train 2, . .. , the nth echo from the echo train N, or the like, may be filled intoa same region (e.g., the region 1).

As exemplified in FIG. 8-B, the ETL of the echo train may be 4, and thek-space may be divided into 4 regions. As illustrated, the phaseencoding lines may be indicated by the lines filled with differentcolors (e.g., black, grey, or the like). The lines filled with a samecolor may be in different regions, while the lines filled with differentcolors may be in a same region. Echoes from the same echo train may befilled in the positions of the phase encoding lines with a same color.Mere by way of example, the echoes including echo 1, echo 2, echo 3, andecho 4 from the same echo train may be filled into the phase encodinglines with the black color. Echoes from different echo trains butlocated in a same position of the echo train may be filled into a sameregion. Merely by way of example, the size of the k-space may be set as128×128. A first echo train may include echo 1, echo 2, echo 3, and echo4, and the four echoes may be filled into the positions of which thephase encoding lines (ky) may be −128, −64, 0, 64, respectively. Asecond echo train may include echo 1′, echo 2′, echo 3′, and echo 4′,and the four echoes may be filled into the positions of which the phaseencoding lines (ky) may be −127, −63, 1, 65, respectively. Other echoesof echo trains may be filled into the regions in the same way.

FIG. 9-A and FIG. 9-B show an exemplary diagram of a method of dividingthe k-space according to some embodiments of the present disclosure. Asillustrated, kx may represent the frequency encoding direction and kymay represent the phase encoding direction. As shown in FIG. 9-B, thek-space may be divided into a plurality of regions including region 1,region 2, . . . , region N−1, and region N. The upper diagram of FIG.9-A may represent two regions of the k-space, and i and i+1 mayrepresent the serial numbers of the regions. In some embodiments, thek-space may be divided into a plurality of regions just like region iand region i+1 along a dividing direction. If the k-space istwo-dimensional, the dividing direction may be the phase encodingdirection. If the k-space is three-dimensional, the dividing directionmay be the first phase encoding direction, the second phase encodingdirection, or the direction that is any linear combination of the firstphase encoding direction and the second phase encoding direction. In theembodiment illustrated in FIG. 9-A, the k-space may be divided into aplurality of regions along the dividing direction (e.g., the phaseencoding direction). As shown in the upper diagram of FIG. 9-A, theregion with backward slashes within the region i and the region withbackward slashes within the region i+1 may overlap (may be defined as an“overlapping region”). Similarly, the region with forward slashes withinthe region i+1, and the region with forward slashes within the regioni+2 (not shown in FIG. 9-A) may overlap, and the region with forwardslashes within the region i−1 (not shown in FIG. 9A), and the regionwith forward slashes within the region i may overlap. Further similarly,a plurality of overlapping regions may occur between two adjacentregions of the k-space.

In some embodiments, the size of the region may be fixed or variable.The sizes of the regions may be the same or different with each other.In some embodiments, the sizes of the regions may be set by the defaultof the system, or set by a user (e.g., an operator) based on one or morerelated parameters (e.g., number of the echoes of an echo line generatedby the FSE sequence, contrast requirement of the final image, or thelike, or a combination thereof). For example, the sizes of the regionsmay be set as increasing or decreasing in order (e.g., the size ofregion 2 may be larger than that of region 1, or the size of region 2may be smaller than that of region 1). As another example, the sizes ofthe regions near the center of the k-space may be smaller than that ofthe regions far away from the center of the k-space. As a furtherexample, the sizes of the regions may be symmetrical with respect to thecenter of the k-space. In some embodiments, the size of the overlappingregion may be fixed or variable. The sizes of the overlapping regionsmay be the same or different with each other. For example, in oneregion, the two overlapping regions may be symmetrical or unsymmetricalwith respect to the center axis of the region.

It should be noted that the above description is merely provided for thepurposes of illustration, and not intended to limit the scope of thepresent disclosure. For persons having ordinary skills in the art,multiple variations and modifications may be made under the teaching ofthe present invention. For example, in some embodiments, the k-space maybe derived from not only rectangular coordinate system but alsonon-rectangular coordinate systems, for example from polar coordinatesystem. The k-space may be divided into several regions along the radialdirection. However, those variations and modifications do not departfrom the scope of the present disclosure.

FIG. 10-A and FIG. 10-B show an exemplary diagram of a method ofdividing the k-space according to some embodiments of the presentdisclosure. As illustrated in FIG. 10-A and FIG. 10-B, the k-space maybe divided into a plurality of regions. The plurality of regions mayinclude a first region including the center of the k-space (e.g., regionB, region B′) and a second region different from the first region. Forexample, the second region may be a region not including the center ofthe k-space. As another example, the second region may be a regionincluding the center of the k-space but with a different size from thefirst region. In some embodiments, the second region may include aplurality of regions (e.g., region A, region C, region A′, region C′, orthe like). In some embodiments, the k-space may be divided into aplurality of regions along a dividing direction. The dividing directionmay be the first phase encoding direction, the second phase encodingdirection, or any linear combination of the first phase encodingdirection and the second phase encoding direction. In some embodiments,as shown in FIG. 10-A, in a rectangular coordinate system, the k-spacemay be divided along the phased encoding direction. In some embodiments,as shown in FIG. 10-B, in a polar coordinate system, the k-space maydivided along the radial direction. In some embodiments, the pluralityof regions may include a plurality of overlapping regions between anytwo adjacent regions (see FIGS. 9-A and 9-B). In some embodiments, asshown in FIG. 10-A and FIG. 10-B, the plurality of regions may becontinuous with no overlapping regions.

FIG. 11 provides a schematic diagram illustrating filling data linesinto the k-space according to some embodiments of the presentdisclosure. The X-axis represents phase encoding direction, and therange of the phase encoding direction may be [−127, 128] as shown inFIG. 11. The Y-axis represents the intensity of the echo signals. Insome embodiments, a plurality groups of data lines (also called “echoline”) may be filled into the k-space. As used herein, a group of datalines may include a plurality of data lines, and a data line may includea plurality of echoes (or “echo signals”, see FIG. 7). The group of datalines may be acquired continuously by a single FSE sequence. As usedherein, during an acquisition process, a group of data lines may beacquired by the single FSE sequence and filled into a region of thek-space (e.g., the region B including the center of the k-spaceillustrated in FIG. 10-A) along a filling direction (e.g., a fillingdirection described in FIG. 13-A or a filling direction described inFIG. 13-B). In some embodiments, for the plurality of groups of datalines, the number of the data lines in one group of data lines may bethe same with that of the data lines in any other group of data lines.As shown in FIG. 9-A through FIG. 10-B, the k-space may be divided intoa plurality of regions, including region 1, region 2, . . . , region N−1and region N. In some embodiments, one region may correspond to one FSEsequence, and a group of data lines generated by one FSE sequence may befilled into the region. For example, as shown in FIG. 11, a first groupof data lines D1 generated by a first FSE sequence (not shown in FIG.11) may be filled into the region 1. Similarly, a second group D2, athird group D3, and a fourth group D4 generated by a second FSEsequence, a third FSE sequence and a fourth FSE sequence, respectively,may be filled into the region 2, region 3, and region 4 respectively.

In some embodiments, the range of the phase encoding direction may bedivided into two sections including [−127, 0] and [0, +128]. In thesection [−127, 0], the groups of data lines may be filled into theregions along a first filling direction, e.g., along the phase encodingdirection or along the direction opposite to the phase encodingdirection. In the section [0, +128], the groups of data lines may befilled into the regions along a second filling direction that isopposite to the first filling direction. For example, as illustrated,the filling directions of the first group D1 and the second group D2 maybe the same. In some embodiments, the number of the data lines in thefirst group D1 may be the same or different from that in the secondgroup D2. In some embodiments, there may be a mathematical relationshipbetween the number of the data lines in the first group D1 and that inthe second group D2. In some embodiments, two adjacent regions mayinclude an overlapping region (see FIG. 9-A and FIG. 9-B). The groups ofdata lines filled into the adjacent regions may include one or moreoverlapping data lines. For example, the first group D1 and the secondgroup D2 may include at least one overlapping data line along a samefilling direction (e.g., phase encoding 1). As another example, thethird group D3 and the fourth group D4 may also include at least oneoverlapping data line along a same filling direction (e.g., phaseencoding 2). Similarly, other groups of data lines may be filled intothe other regions of the k-space in the same way.

As is known, in a region near the center of the k-space (ky=0), thephase encoding gradient is low and from the center to the two end points(e.g., ky=−127 or ky=+128 in the case that the range of the k-spacealong the phase encoding direction is [−127, 128]), the phase encodinggradient increases gradually. The intensity of the echo signal mayattenuate with the increase of the phase encoding gradient. In theregion near the center of the k-pace, the intensity of the echo signalsmay be high and the signals may impact the final image contrast or imagequality. In some embodiments, as shown in FIG. 11, the first group ofdata lines D1 and the third group of data lines D3 are filled into theregions near the center of k-space. The filling direction of the firstgroup D1 is opposite to that of the third group D3, and the two groupsmay include at least an overlapping data line (e.g., the zero-phaseencoding (ky=0)).

In some embodiments, at least three groups of data lines may begenerated by N FSE sequences. Among the three groups of data lines, atleast two groups of data lines may include the data line of which thephase encoding is the zero-phase encoding (the center of the k-space(ky=0)), at least one group of data lines of which the phase encoding islarger or smaller than the zero-phase encoding. For example, if N=3, twogroups of data lines may include the data line of which the phaseencoding direction is the zero-phase encoding, and one group of datalines of which the phase encoding is larger or smaller than thezero-phase encoding. As another example, if N=4, two groups of datalines may include the data line of which the phase encoding direction isthe zero-phase encoding, and the other two groups of data lines of whichthe phase encoding is larger or smaller than the zero-phase encoding.

In some embodiments, for the data lines filled in the overlappingregions, a correction may be performed. For example, for the overlappingregion between region 1 and region 2, the correction may be performedaccording to Equation (1) and Equation (2) below:A=A1+A2,  Equation (1)andφ=φ1+φ2,  Equation (2)where A refers to the amplitude of echoes in the overlapping region, A1refers to the amplitude of the echoes from region 1 filled into theoverlapping region, A2 refers to the amplitude of the echoes from region2 filled into the overlapping region, φ refers to the phase value of theechoes in the overlapping region, φ1 refers to the phase value of theechoes from region 1 filled into the overlapping region, φ2 refers tothe phase value of the echoes from region 2 filled into the overlappingregion.

As another example, the correction may be performed according toEquation (3) and Equation (4) below:A=A1,  Equation (3)andφ=φ1.  Equation(4)

As a further example, the correction may be performed according toEquation (5) and Equation (6) below:A=A2,  Equation (5)andφ=φ2.  Equation (6)

As a still further example, the correction may be performed according toEquation (7) and Equation (8) below:A=α1×A1+α2×A2,  Equation (7)andφ=α1×φ1+α2×φ2.  Equation (8)

As used herein, α1 and α2 refer to the weighting coefficients of A1 andA2 respectively, and α1+α2=1, 0≤α1≤1, 0≤α2≤1. In some embodiments, theweighting coefficients α1 and α2 may be determined using Equation (9)and Equation (10) below:

$\begin{matrix}{{\alpha = {0.75 - {0.25 \times {\cos( \frac{x - x_{0}}{x_{0}} )} \times \pi}}},{and}} & {{Equation}\mspace{14mu}(9)} \\{{\alpha = {0.25 + {0.25 \times {\cos( \frac{x - x_{0}}{x_{0}} )} \times \pi}}},} & {{Equation}\mspace{14mu}(10)}\end{matrix}$

As used herein, the direction pointing from the overlapping regiontoward the non-overlapping region may be defined as the positivedirection, and the connection point of the overlapping region and thenon-overlapping region may be defined as the origin of coordinates. InEquations (9) and (10), x0 refers to the x-coordinate of the center ofthe overlapping region, x refers to the x-coordinate of the overlappingregion, α represents a weighting coefficient and α1=α.

In some embodiments, for an echo signal filled into the overlappingregion, the weighting coefficient may be inversely proportional to thedistance between the echo signal and the central axis of the region. Thesmaller the distance between the echo signal and the central axis of theregion is, the larger the weighting coefficient may be, e.g., the closerto 1 the weighting coefficient may be; while the larger the distancebetween the echo signal and the central axis of the region is, thesmaller the weighting coefficient may be, e.g., the closer to 0 theweighting coefficient may be.

This description is intended to be illustrative, and not to limit thescope of the present disclosure. Many alternatives, modifications, andvariations will be apparent to those skilled in the art. The features,methods, and other characteristics of the exemplary embodimentsdescribed herein may be combined in various ways to obtain additionaland/or alternative exemplary embodiments. For example, the value of N isnot specific and may be adjusted under different situations. As anotherexample, the overlapping region between the adjacent regions is notnecessary, thus the overlapping data lines are not necessary.

FIG. 12 provides another schematic diagram illustrating filling datalines into the k-space according to some embodiments of the presentdisclosure. As shown in FIG. 10-A and FIG. 10-B, the k-space may bedivided into a first region including the center of the k-space (e.g.,region B, region B′) and a second region different from the first region(e.g., region A, region C, region A′, region C′, or the like). As shownin FIG. 12, a plurality groups of data lines generated by a plurality ofFSE sequences may be filled into the regions. In some embodiments, thefirst region (e.g., region B) and/or the second region (e.g., region A,or region C) may be divided into one or more segments (also referred toas “portion”). In some embodiments, one segment may correspond to onegroup of data lines. For example, as shown in FIG. 12, region A may bedivided into segment S1, segment S2, and segment S3. Region B may bedivided into segment S4 and segment S5. Region C may be divided intosegment S6, segment S7, and segment S8. In some embodiments, the fillingdirection of at least a segment of the first region may be opposite tothe filling direction of at least a portion of the second region. Forexample, the filling direction of segment S5 in region B is opposite tothe filling direction of segment S6 in region C. In some embodiments,the filling direction of two adjacent segments may be opposite in orderto avoid a sudden jump of data points (details may be found in, forexample, FIG. 15-A and FIG. 15-B). As used herein, the phrase “twoadjacent segments” may represent that one segment abuts the othersegment. For example, as shown in FIG. 12, the filling directions ofsegment S1 and segment S2 in region A may be opposite.

FIG. 13-A and FIG. 13-B provide schematic diagrams illustrating fillingechoes into the k-space according to some embodiments of the presentdisclosure. As illustrated, an echo line (also referred to as “dataline” or “echo train”) may include a plurality of echoes, e.g., echo #1,echo #2, echo #3, echo #4, and echo #5. For brevity, as used herein,echo #1 may refer to an echo of which the echo time may be shortest, andecho #5 may refer to an echo of which the echo time may be longest. Insome embodiments, a FSE sequence may generate a group of echo lines, andeach echo line may include a plurality of echoes including, for example,echo #1, echo #2, echo #3, echo #4, and echo #5. The groups of echolines generated from a plurality of FSE sequences may be filled into theregions of the k-space along the filling direction (e.g., the phaseencoding direction) as illustrated in FIG. 13-A, or along the directionopposite to the filling direction (e.g., the phase encoding direction)as illustrated in FIG. 13-B.

FIG. 14-A and FIG. 14-B illustrate the filling of echoes into a regionnear the center of the k-space according to some embodiments of thepresent disclosure. For the first region including the center of thek-space, in some embodiments, only one group of echo lines (also called“data line”) may be filled into the first region in the way thatillustrated in FIG. 13-A or FIG. 13-B. The group of echo lines may begenerated by one FSE sequence and may be filled into the first regionnear the center of k-space continuously along the filling direction(e.g., the phase encoding direction) or along the direction opposite tothe filling direction (e.g., the phase encoding direction). In someembodiments, more than one group of echo lines may be filled into thefirst region, that is, echo lines from different FSE sequences may befilled into the first region. In some embodiments, if the echo with theeffective TE (descriptions regarding effective TE may be found in FIG.7) occurs at the beginning or the end of the echo line, the echoes of anecho line may be filled into the first region in the way illustrated inFIG. 14-A. As illustrated, the filled dots represent a first group ofecho lines of which each echo line includes echo #1, echo #2, echo #3,echo #4 and echo #5, while the open dots represent a second group ofecho lines of which each echo line includes echo #1′, echo #2′, echo#3′, echo #4′ and echo #5′. As shown in FIG. 14-A, the first region maybe divided into two segments including a first segment and a secondsegment, the first group of echo lines may be filled into the firstsegment along the filling direction (e.g., the phase encodingdirection), and the second group of echo lines may be filled into thesecond segment along the direction opposite to the filling direction(e.g., the phase encoding direction). The two groups of echo lines maybe symmetrical relative to the center of the k-space.

In some embodiments, if the echo with the effective TE does not occur atthe beginning or the end of the echo line, however for example, is setas the second echo of the echo line (e.g., echo #2 and echo #2′) asillustrated in FIG. 14-B. The first group of echo lines may be filledinto the first region along the filling direction (e.g., the phaseencoding direction). The second group of echo lines may be filled intothe first region along the direction opposite to the filling direction(e.g., the phase encoding direction). Because that the echoes witheffective TE occur as the echo #2 and echo #2′ and are filled near thecenter of the k-space, during the filling process, an overlapping partbetween the first group of echo lines and the second group of echo linesnear the center of k-space may form. Echo #1 of the first group of echolines may overlap with echo #3′ of the second group of echo lines.Similarly, echo #1′ of the second group of echo lines may overlap withecho #3 of the first group of echo lines. The filled echoes may besymmetrical relative to the center of k-space. Regarding the overlappingpart between the first group of echo lines and the second group of echolines, further data processing (e.g., a weighted averaging process) maybe performed.

This description is intended to be illustrative, and not to limit thescope of the present disclosure. Many alternatives, modifications, andvariations will be apparent to those skilled in the art. The features,methods, and other characteristics of the exemplary embodimentsdescribed herein may be combined in various ways to obtain additionaland/or alternative exemplary embodiments. For example, see FIG. 14-B,the overlapping part between the first group and the second group is notnecessary. The overlapping echoes (e.g., echo #1 of the first group ofdata lines and echo #3′ of the second group of data lines) may be filledin an adjacent position with each other. In this embodiment, any furtherdata processing is not necessary. As another example, the echoes witheffective TE may be set as any echo of the echo lines, such as echo #3,echo #4, or the like.

FIG. 15-A and FIG. 15-B illustrate the filling of echoes into the regionnot including the center of the k-space according to some embodiments ofthe present disclosure. As illustrated, the second region not includingthe center of the k-space may be divided into a plurality of segments,including segment 1, segment 2, or the like. In some embodiments, theplurality of segments may include at least two adjacent segments, forexample, segment 1 and segment 2. As shown in FIG. 15-A, in segment 1,the echo lines are filled along the direction opposite to the fillingdirection (e.g., the phase encoding direction), while in segment 2, theecho lines are filled along the filling direction (e.g., the phaseencoding direction). For brevity, two echo lines are filled into segment1 or segment 2, it should be noted that more than two echo lines may befilled into the segments. For other adjacent segments, echo lines may befilled in the same way to avoid jump of data points and keep the filleddata smoothly.

In some embodiments, the adjacent segments may include an overlappingportion (see FIG. 9-A and FIG. 9-B). The echo lines may be filled intothe adjacent segments along a same direction (e.g., the phase encodingdirection or the direction opposite to the phase encoding direction).For the overlapping portion, some overlapping echoes or some overlappingparts of data lines may occur. The overlapping echoes or the parts ofdata lines may be further processed (e.g., a weighting process accordingto, for example, Equations (1)-(10)).

FIG. 16-A and FIG. 16-B are exemplary schematic diagrams of correctingthe data filled into the k-space according to some embodiments of thepresent disclosure. As illustrated, region B may refer to the regionincluding the center of the k-space, while region A and region C mayrefer to the regions not including the center of the k-space. The firstset of data lines (or referred to as “echo line” or “echo train”) markedwith {circle around (1)} may be filled into the regions. The solid linemay refer to a group of data lines that is filled into the region alongthe filling direction (e.g., the phase encoding direction), while thedashed line may refer to a group of data lines that is filled into theregion along the direction opposite to the filling direction (e.g.,opposite to the phase encoding direction). Intensity attenuation mayoccur along the data lines. The second set of data lines marked with{circle around (2)} may be filled into the regions of the k-space alonga filling direction that is opposite to that of the set marked with{circle around (1)}. It means that at any point of the phase encoding,the filled echo signals may be repeatedly acquired (e.g., at leasttwice), and a mathematical processing, e.g., a weighted averagingprocess, may be performed regarding the echo signals.

As illustrated in FIG. 16-B, for a portion (also referred to as a“segment”) of a region (see, for example, FIG. 12), suppose that theechoes may be filled into the k-space along the phase encodingdirection. As used herein, the region may include the region B, theregion A, the region C, or any region divided from the k-space. As usedherein, a portion of the region may refer to a portion in which a groupof data lines may be filled (see details in FIG. 12). As illustrated inFIG. 16-B, the phase encoding range of the portion may be PE₁˜PE_(ETL),and a group of data lines may be filled in the portion. For brevity,only a first data line (also referred to as an “echo train”) includingecho 1, echo 2, . . . , echo x, . . . , echo ETL filled into the portionalong the phase encoding direction is shown. For a phase encoding sitePEx in the portion, an echo x may be filled in the phase encoding site.In some embodiments, a second data line including echo 1′, echo 2′, . .. , echo y, . . . , echo ETL′ may be filled into the portion along thedirection opposite to the phase encoding direction. As illustrated, anecho y may be filled in the phase encoding site PEx. As used herein,y=ETL−x+1, 1≤x≤ETL, 1≤y≤ETL. A weighted averaging process may beperformed on the echo x and echo y filled at the PEx site, and theeffect of signal intensity attenuation on image quality may be reducedor eliminated.

This description is intended to be illustrative, and not to limit thescope of the present disclosure. Many alternatives, modifications, andvariations will be apparent to those skilled in the art. The features,methods, and other characteristics of the exemplary embodimentsdescribed herein may be combined in various ways to obtain additionaland/or alternative exemplary embodiments. For example, besides the phaseencoding direction, the echoes may be filled into the k-space along anylinear combination direction of the first and the second encodingdirections (e.g., the radial orientation).

FIG. 17-A through FIG. 17-D illustrate four exemplary images produced bythe data acquired from the abdomen with different image producingprocedures according to some embodiments of the present disclosure. FIG.17-A and FIG. 17-B show two images of the abdomen (fat saturation)produced by the data that was filled into the k-space by a traditionalmethod and by the filling method disclosed in the present disclosurerespectively. FIG. 17-C and FIG. 17-D show two images of the abdomen (nofat saturation) produced by the data that were filled into the k-spaceby the traditional method and by the filling method disclosed in thepresent disclosure respectively. As shown in FIG. 17-A and FIG. 17-C,The images of the abdomen produced by the data that were filled into thek-space by the traditional method had some defects or artifacts becauseof the breath interference of the subject being scanned. For example,the imaging of the liver area was not clear, and it was difficult toidentify the vascular profile. During the process for obtaining theimages shown in FIG. 17-B and FIG. 17-D, the k-space was divided into aplurality of regions, among which two adjacent regions include anoverlapping region (see FIG. 9-A and FIG. 9-B). In the overlappingregion, a weighted averaging process was performed on the filled data.It may be seen that the structures of the abdominal area and the liverarea were clear, the details were clearly visible, the vascular profilewas improved, and the artifacts of the bright band on the border werealmost invisible. The image producing procedure disclosed in the presentdisclosure may be effective in reducing signal abnormalities caused bybreathing, and decreasing the sensitivity of image quality to motion,regardless of with or without fat saturation.

FIG. 18-A and FIG. 18-B show two images of the neck produced by the datathat is filled into the k-space by a traditional method described inFIG. 8-A and FIG. 8-B and by the filling method disclosed in the presentdisclosure respectively. As shown in FIG. 18-A, the image produced bythe data that was filled into the k-space by the traditional method hadobvious cerebrospinal fluid (CSF) pulsation artifacts. As shown in FIG.18-B, during the process for obtaining the image, the k-space wasdivided into a plurality of regions including a first region includingthe center of the k-space and a second region different form the firstregion (see FIG. 10-A and FIG. 10-B). It may be seen that the CSFpulsation artifact was significantly reduced, and meanwhile the clarityof the structure of the intervertebral disc was improved. The imageproducing procedures in the present disclosure may be effective inreducing artifacts induced by the periodic motion of CSF.

It should be noted that the above description is merely provided for thepurposes of illustration, and not intended to limit the scope of thepresent disclosure. The image producing procedures in the presentdisclosure may be effective in reducing, removing or eliminating othertypes of motion artifacts including, for example, the vascularpulsation, heart movement, and random motion of the subject beingscanned, or the like, or any combination thereof. The image producingprocedures in the present disclosure may be applied to whole body MRimaging, and the images produced may have more clear structural details.

Having thus described the basic concepts, it may be rather apparent tothose skilled in the art after reading this detailed disclosure that theforegoing detailed disclosure is intended to be presented by way ofexample only and is not limiting. Various alterations, improvements, andmodifications may occur and are intended to those skilled in the art,though not expressly stated herein. These alterations, improvements, andmodifications are intended to be suggested by this disclosure, and arewithin the spirit and scope of the exemplary embodiments of thisdisclosure.

Moreover, certain terminology has been used to describe embodiments ofthe present disclosure. For example, the terms “one embodiment,” “anembodiment,” and/or “some embodiments” mean that a particular feature,structure or characteristic described in connection with the embodimentis included in at least one embodiment of the present disclosure.Therefore, it is emphasized and should be appreciated that two or morereferences to “an embodiment” or “one embodiment” or “an alternativeembodiment” in various portions of this specification are notnecessarily all referring to the same embodiment. Furthermore, theparticular features, structures or characteristics may be combined assuitable in one or more embodiments of the present disclosure.

Further, it will be appreciated by one skilled in the art, aspects ofthe present disclosure may be illustrated and described herein in any ofa number of patentable classes or context including any new and usefulprocess, machine, manufacture, or composition of matter, or any new anduseful improvement thereof. Furthermore, aspects of the presentdisclosure may take the form of a computer program product embodied inone or more computer readable media having computer readable programcode embodied thereon.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including electro-magnetic, optical, or thelike, or any suitable combination thereof. A computer readable signalmedium may be any computer readable medium that is not a computerreadable storage medium and that may communicate, propagate, ortransport a program for use by or in connection with an instructionexecution system, apparatus, or device. Program code embodied on acomputer readable signal medium may be transmitted using any appropriatemedium, including wireless, wireline, optical fiber cable, RF, or thelike, or any suitable combination of the foregoing.

Computer program code for carrying out operations for aspects of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C#, VB. NET,Python or the like, conventional procedural programming languages, suchas the “C” programming language, Visual Basic, Fortran 2003, Perl, COBOL2002, PHP, ABAP, dynamic programming languages such as Python, Ruby andGroovy, or other programming languages. The program code may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider) or in a cloud computing environment or offered as aservice such as a Software as a Service (SaaS).

Furthermore, the recited order of processing elements or sequences, orthe use of numbers, letters, or other designations therefore, is notintended to limit the claimed processes and methods to any order exceptas may be specified in the claims. Although the above disclosurediscusses through various examples what is currently considered to be avariety of useful embodiments of the disclosure, it is to be understoodthat such detail is solely for that purpose, and that the appendedclaims are not limited to the disclosed embodiments, but, on thecontrary, are intended to cover modifications and equivalentarrangements that are within the spirit and scope of the disclosedembodiments. For example, although the implementation of variouscomponents described above may be embodied in a hardware device, it mayalso be implemented as a software only solution—e.g., an installation onan existing server or mobile device.

Similarly, it should be appreciated that in the foregoing description ofembodiments of the present disclosure, various features are sometimesgrouped together in a single embodiment, figure, or description thereoffor the purpose of streamlining the disclosure aiding in theunderstanding of one or more of the various inventive embodiments. Thismethod of disclosure, however, is not to be interpreted as reflecting anintention that the claimed subject matter requires more features thanare expressly recited in each claim. Rather, inventive embodiments liein less than all features of a single foregoing disclosed embodiment.

In some embodiments, the numbers expressing quantities of ingredients,properties such as molecular weight, reaction conditions, and so forth,used to describe and claim certain embodiments of the application are tobe understood as being modified in some instances by the term “about,”“approximate,” or “substantially.” For example, “about,” “approximate,”or “substantially” may indicate ±20% variation of the value itdescribes, unless otherwise stated. Accordingly, in some embodiments,the numerical parameters set forth in the written description andattached claims are approximations that may vary depending upon thedesired properties sought to be obtained by a particular embodiment. Insome embodiments, the numerical parameters should be construed in lightof the number of reported significant digits and by applying ordinaryrounding techniques. Notwithstanding that the numerical ranges andparameters setting forth the broad scope of some embodiments of theapplication are approximations, the numerical values set forth in thespecific examples are reported as precisely as practicable.

Each of the patents, patent applications, publications of patentapplications, and other material, such as articles, books,specifications, publications, documents, things, and/or the like,referenced herein is hereby incorporated herein by this reference in itsentirety for all purposes, excepting any prosecution file historyassociated with same, any of same that is inconsistent with or inconflict with the present document, or any of same that may have alimiting affect as to the broadest scope of the claims now or laterassociated with the present document. By way of example, should there beany inconsistency or conflict between the description, definition,and/or the use of a term associated with any of the incorporatedmaterial and that associated with the present document, the description,definition, and/or the use of the term in the present document shallprevail.

In closing, it is to be understood that the embodiments of theapplication disclosed herein are illustrative of the principles of theembodiments of the application. Other modifications that may be employedmay be within the scope of the application. Thus, by way of example, butnot of limitation, alternative configurations of the embodiments of theapplication may be utilized in accordance with the teachings herein.Accordingly, embodiments of the present application are not limited tothat precisely as shown and described.

We claim:
 1. A method of obtaining an NMR image, the method comprising:dividing k-space into a plurality of regions along a dividing direction,the plurality of regions comprising a first region including a center ofthe k-space and a second region adjacent to but different from the firstregion, wherein the first region and the second region partially overlapwith each other; scanning an object using a plurality of samplingsequences to acquire a plurality of groups of data lines along thedividing direction, with each group of data lines corresponding to oneof the plurality of sampling sequences and filled into a region of theplurality of regions along a filling direction, wherein a data linecomprises a plurality of echo signals corresponding to a plurality ofecho times respectively and wherein the filling direction is phaseencoding direction in magnetic resonance imaging and the filingdirection of at least a portion of the first region is opposite to thefilling direction of at least a portion of the second region; andreconstructing the plurality of groups of data lines filled into thek-space to obtain an NMR image of the object.
 2. The method of claim 1,the dividing direction comprising a first phase encoding direction, asecond phase encoding direction, a linear combination of the first phaseencoding direction and the second phase encoding direction, or a radialdirection.
 3. The method of claim 1, wherein the filing directioncomprises a first direction that is along the dividing direction oropposite to the dividing direction, and a second direction that isopposite to the first direction.
 4. The method of claim 3, the pluralityof groups of data lines comprising a first group of data lines and asecond group of data lines, wherein the first group of data lines arefilled into the first region along the first direction, and the secondgroup of data lines are filled into the first region along the seconddirection.
 5. The method of claim 4, the first group of data lines andthe second group of data lines are symmetric with respect to the centerof the k-space.
 6. The method of claim 5, the first group of data linesand the second group of data lines each comprising one or more datalines and the one or more data lines from the first group of data linesand the second group of data lines have same phase encoding.
 7. Themethod of claim 6, further comprising: performing a weighted averagingprocess on the one or more data lines with the same phase encoding. 8.The method of claim 3, the plurality of groups of data lines comprisinga third group of data lines and a fourth group of data lines, wherein afirst portion of the first region abuts a second portion of the secondregion, the third group of data lines are filled into the first portionalong the first direction, and the fourth group of data lines are filledinto the second portion along the second direction.
 9. The method ofclaim 3, further comprising: dividing the second region into a pluralityof portions, the plurality of portions comprising a third portion and afourth portion that abuts the third portion, wherein a fifth group ofdata lines are filled into the third portion along the first direction,and a sixth group of data lines are filled into the fourth portion alongthe second direction.
 10. The method of claim 3, further comprising:performing a correction of at least some groups of the plurality ofgroups of data lines based on the echo times of the echo signals. 11.The method of claim 10, the performing a correction comprising:identifying a fifth portion in a third region of the plurality ofregions, the fifth portion being filled with a seventh group of datalines along the first direction; obtaining an eighth group of datalines; filling the eighth group of data lines into the fifth portion ofthe third region along the second direction; and performing a weightedaveraging process on the seventh group of data lines and the eighthgroup of data lines.
 12. The method of claim 1, the plurality of groupsof data lines comprising at least three groups of data lines, whereintwo groups of data lines of the three groups of data lines include adata line corresponding to zero phase encoding, phase encodings of theother one group of data lines of the three groups of data lines arelarger than or less than the zero phase encoding.
 13. The method ofclaim 1, the acquiring a plurality of groups of data lines comprising:acquiring two groups of data lines using two sampling sequences, whereinthe filling directions of the two groups of lines are the same oropposite, and wherein the two groups of data lines include one or moredata lines with a same phase encoding.
 14. The method of claim 1, thesampling sequence comprising a fast spin echo sequence, a half-Fourieracquisition single-shot turbo spin-echo, a turbo gradient spin echosequence, or an echo planar imaging sequence.
 15. The method of claim 1,wherein the second region does not include the center of the k-space.16. The method of claim 1, wherein each group of data lines of theplurality of groups of data lines comprises a same number of data lines.17. A method comprising: dividing k-space into a plurality of regionsalong a dividing direction, the plurality of regions comprising a firstregion and a second region adjacent to the first region, with at leastone of the first region and the second region including at least portionof a center of the k-space, and wherein the first region and the secondregion partially overlap with each other; scanning an object using aplurality of sampling sequences to acquire a plurality of groups of datalines along the dividing direction, with each group of data linescorresponding to one of the plurality of sampling sequences and filledinto a region of the plurality of regions along a filing direction,wherein a data line comprises a plurality of echo signals correspondingto a plurality of echo times respectively and wherein the fillingdirection is phase encoding direction in magnetic resonance imaging andthe filing direction of at least a portion of the first region isopposite to the filling direction of at least a portion of the secondregion; and reconstructing the plurality of groups of data lines filledinto the k-space to obtain an NMR image of the object.
 18. A system forobtaining an NMR image, the system comprising: a region division blockconfigured to divide k-space into a plurality of regions along adividing direction, the plurality of regions comprising a first regionincluding a center of the k-space and a second region adjacent to butdifferent from the first region, wherein the first region and the secondregion partially overlap with each other; an MRI scanner configured toscan an object using a plurality of sampling sequences to acquire aplurality of groups of data lines along the dividing direction, witheach group of data lines corresponding to one of the plurality ofsampling sequences and filled into a region of the plurality of regionsalong a filing direction using a filling block of the system, wherein adata line comprises a plurality of echo signals corresponding to aplurality of echo times respectively and wherein the filling directionis phase encoding direction in magnetic resonance imaging and the filingdirection of at least a portion of the first region is opposite to thefilling direction of at least a portion of the second region; an imagereconstruction block configured to reconstruct the plurality of groupsof data lines filled into the k-space to obtain an NMR image of theobject; wherein the dividing direction comprises a first phase encodingdirection, a second phase encoding direction, a linear combination ofthe first phase encoding direction and the second phase encodingdirection, or a radial direction.
 19. The system of claim 18, wherein afirst direction is along the dividing direction or opposite to thedividing direction, and a second direction is opposite to the firstdirection, wherein the plurality of groups of data lines comprises afirst group of data lines and a second group of data lines, wherein thefirst group of data lines are filled into the first region along thefirst direction, and the second group of data lines are filled into thefirst region along the second direction.